Related Stories

Addictive non-craving The weight gain that often follows giving up smoking can deter some people from quitting. Now scientists have discovered exactly how nicotine causes weight loss.

The research, led by Professor Marina Picciotto of Yale University in the USA, may eventually lead to drugs that help smokers to give up without putting on weight and could help combat obesity in non-smokers too.

She says nicotine seems to lower their 'set weight', and once they give up the weight returns to normal.

In their study the researchers gave nicotine to mice daily for 30 days and found that the mice reduced their food intake by nearly 50 per cent and lost 15 to 20 per cent of their body fat.

Previous research has shown the effects of nicotine in the brain are due to it binding to the beta 2 receptor, which is responsible for the intense craving that makes it so addictive.

Therefore, Picciotto and her team expected beta 2 would underlie the effect of nicotine on appetite too.

To their surprise, they discovered that a rarer receptor, beta 4, was the one involved. Significantly, they found beta 4 receptors were present on nerve cells in particular parts of a brain region (the hypothalamus) known to be concerned with feeding behaviour.

Picciotto says these receptors actually aren't intended for nicotine, but for acetyl choline, a natural neurotransmitter involved in a host of processes including muscle activation

"One of the fascinating things about this work is that it shows that acetyl choline has a role in feeding behaviour," she says.

Suppression without the addiction

The researchers believe this will open up the possibility of designing drugs to produce appetite suppression, without the addictive side-effects of nicotine.

"Many people say they won't quit smoking because they'll gain weight. Ultimately, we would like to help people maintain their body weight when they kick the habit and perhaps help non-smokers who are struggling with obesity," says Picciotto.

But she cautions that potential drugs would have to be extensively tested for safety. "Nicotine won't solve obesity - the effects are too small," she says, "but it may help".

She is optimistic that the results will be applicable to humans, although this remains to be tested.

Professor Andrew Lawrence of the Florey Neuroscience Institutes in Melbourne says Picciotto's team "have carried out a very elegant series of experiments".

He thinks the appetite suppressant effects may also help schizophrenia patients on antipsychotic drugs, which have a side-effect of putting on weight.

"There is poor compliance, as these drugs cause marked weight gain," he says. "Something like this may help."